Black holes: They're the most destructive monsters in the universe. We already knew they can be powerfully massive. Now scientists say they've found the most massive ones yet, as reported in the journal Nature.

How big?

The mass of each is about 10 billion times the mass of our sun. The previous black hole record holder, first measured in 1977, has a mass of about 6 billion suns.

And for each black hole, the "event horizon" – basically areas from which nothing can escape their gravity – is about five times the distance between our sun and Pluto.

"We started this search several years ago," said black hole hunter Chung-Pei Ma of the University of California, Berkeley. Using Hawaii's huge Keck telescope, and the Gemini and McDonald observatories, Ma says her team "targeted the biggest galaxies in the nearby universe because the biggest galaxies are most likely to host the most massive black holes."

One of the newly found black holes is 320 million light-years from Earth in the direction of the constellation Leo, and the other is 336 million light-years away toward the constellation Coma Berenices.

The awesome, overwhelming power behind black holes has captured the fascination of the astronomy world for generations, including great scientific minds such as Stephen Hawking and Albert Einstein. Their mass is so large they create gravity powerful enough to suck in stars, planets and even light. Some experts suspect black holes may be doors that lead to other galaxies or even alternative universes although it has not been proven.

"He's actually working on a Hollywood movie right now with Steven Spielberg," Ma says. "Thorne says if you were to fall into a black hole, the difference between the gravity near your feet and near your head would be so powerful that you'd be torn apart.

"You could try to curl yourself up into a ball, to reduce that gravity difference, but eventually you'd just get torn up."

The discovery underscores what Ma says is one of the many big questions vexing black hole hunters. How do black holes grow? Do the most powerful ones gain mass differently from lesser ones? Is there a limit to how massive black holes can be? Are these newly discovered black holes at the top of the heap?

"We could be near the top," she says. "We should continue observing to see if these black holes are the biggest, or if they're just the tip of an iceberg. Right now we're not sure."